Crystalline forms of pemetrexed diacid and processes for the preparation thereof

ABSTRACT

Provided are crystalline forms of N-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid, pemetrexed diacid, and processes for the preparation thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/893,212, filed Aug. 14, 2007, now U.S. Pat. No. 8,088,919, whichclaims the benefit of U.S. provisional application Ser. Nos. 60/837,303,filed Aug. 14, 2006; 60/860,557, filed Nov. 21, 2006; 60/837,637, filedAug. 15, 2006; 60/860,554, filed Nov. 21, 2006; 60/880,178, filed Jan.11, 2007; 60/958,213, filed Jul. 3, 2007; 60/839,551, filed Aug. 22,2006; 60/845,031, filed Sep. 14, 2006; 60/899,928, filed Feb. 6, 2007;60/936,553, filed Jun. 20, 2007; 60/958,413, filed Jul. 5, 2007;60/847,291, filed Sep. 25, 2006; 60/855,139, filed Oct. 30, 2006;60/880,179, filed Jan. 11, 2007; and 60/958,326, filed Jul. 2, 2007, allof which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention encompasses crystalline forms ofN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid, pemetrexed diacid, and processes for the preparation thereof.

BACKGROUND OF THE INVENTION

Compounds known to have antifolate activity are well recognized aschemotherapeutic agents for the treatment of cancer. In particular,compounds in the folic acid family have various activities at theenzymatic level as they inhibit such enzymes as dehydrofolate reductase,folate polyglutamate synthetase, glycinamide ribonucleotideformyltransferase and thymidylate synthetase.

European publication No. 0434426 (“EP '426”) discloses a class of4-hydroxypyrrolo[2,3-d]pyrimidine-L-glutamic acid derivatives, andstates that these compounds have antifolate activity and anti-tumoreffect. See EP '426, p. 2, II. 33-56. Among them are hydrate crystallineforms of disodium pemetrexed.

Pemetrexed disodium salt heptahydrate is marketed by Eli Lilly andCompany under the trade name ALIMTA® as a sterile lyophilized powder forintravenous administration. This member of the folic acid family hasbeen approved for treatment of malignal pleural mesothelioma and forsecond-line treatment of non small cell lung cancer. See Physicians'Desk Reference, 60th ed., pp. 1722-1728 (2006).

International PCT publication WO 01/14379 discloses hydrate crystallinedisodium pemetrexed.

The preparation of the commerical lyophilized or formulated lyophilizedpemetrexed disodium is disclosed in U.S. Pat. No. 7,138,521. Thispemetrexed disodium is prepared fromN-[4-[2-(2-Amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]L-glutamicacid diethylester p-toluenesulfonic acid salt, which is saponified at apH of between 2.5 to 3.5 to giveN-[4-[2(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid (“pemetrexed diacid”), of the following Formula II:

The pemetrexed diacid is isolated as a wet cake and then combined with 2to 3 equivalents of sodium hydroxide at a pH of between 7 and 9. Theresulting pemetrexed disodium heptahydrate is then isolated from thereaction mixture by precipitation using acetone. The isolated pemetrexeddisodium heptahydrate is then used to prepare the pharmaceuticalcomposition.

Pemetrexed diacid and its preparation is believed to have been describedfor the first time in U.S. Pat. No. 5,344,932.

Formation and isolation ofN-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid from a mixture of water and ethanol having a pH of 2.5-3.5 isdisclosed in U.S. Pat. No. 7,138,521. A similar isolation is disclosedin C. J. Barnett, et al., “A Practical Synthesis of MultitargetedAntifolate LY231514,” Organic Process Research & Development, 3(3):184-188 (1999).

Formation and isolation ofN-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid from an aqueous solution having a pH of 5 is disclosed in U.S. Pat.No. 5,416,211.

Formation and isolation of pemetrexed diacid from an aqueous solution ofthe p-toluenesulfonic acid salt of the corresponding dialkyl estercompound by addition of sodium hydroxide and adjusting the pH to 2.8-3.1is disclosed in U.S. Pat. No. 6,262,262.

The occurrence of different crystal forms (polymorphism) is a propertyof some molecules and molecular complexes. A single molecule may giverise to a variety of solids having distinct physical properties likemelting point, X-ray diffraction pattern, infrared absorptionfingerprint and NMR spectrum. The differences in the physical propertiesof polymorphs result from the orientation and intermolecularinteractions of adjacent molecules (complexes) in the bulk solid.

Accordingly, polymorphs are distinct solids sharing the same molecularformula yet having distinct advantageous and/or disadvantageous physicalproperties compared to other forms in the polymorph family. One of themost important physical properties of pharmaceutical polymorphs is theirsolubility in aqueous solution, which may influence the bioavailabilityof the drug.

These practical physical characteristics are influenced by theconformation and orientation of molecules in the unit cell, whichdefines a particular polymorphic form of a substance that can beidentified unequivocally by X-ray spectroscopy. The polymorphic form maygive rise to thermal behavior different from that of the amorphousmaterial or another polymorphic form. Thermal behavior is measured inthe laboratory by such techniques as capillary melting point,thermogravimetric analysis (TGA) and differential scanning calorimetry(DSC) and can be used to distinguish some polymorphic forms from others.A particular polymorphic form may also give rise to distinctspectroscopic properties that may be detectable by solid state ¹³C NMRspectrometry and infrared spectroscopy.

The discovery of new polymorphic forms of pemetrexed diacid provides anew opportunity to improve the performance of the synthesis of theactive pharmaceutical ingredient (API), pemetrexed disodium, byproducing crystalline forms of pemetrexed diacid having improvedcharacteristics, such as flowability, and solubility. Thus, there is aneed in the art for polymorphic forms of pemetrexed diacid.

SUMMARY OF THE INVENTION

In one embodiment, the invention encompasses crystalline pemetrexeddiacid characterized by data selected from the group consisting of: anX-ray powder diffraction (“PXRD”) pattern with peaks at about 10.0,10.3, 22.0 and 25.7 degrees two-theta±0.2 degrees two-theta, and a PXRDpattern as depicted in FIG. 1.

In another embodiment, the invention encompasses crystalline pemetrexeddiacid characterized by data selected from the group consisting of: aPXRD pattern having peaks at about 5.7, 12.2, 17.2 and 18.4 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.2.

In another embodiment, the invention encompasses a process for preparingthe above crystalline pemetrexed diacid. The process comprises providinga suspension of pemetrexed diacid in an aqueous solvent having a pH ofabout 3, and adjusting the pH of the suspension to about 4.5.

In yet another embodiment, the invention encompasses crystallinepemetrexed diacid characterized by data selected from the groupconsisting of: a PXRD pattern having peaks at about 5.8, 12.4, 18.6 and24.6 degrees two-theta±0.2 degrees two-theta; and a PXRD pattern asdepicted in FIG. 3.

In another embodiment, the invention encompasses crystalline pemetrexeddiacid characterized by data selected from the group consisting of: aPXRD pattern having peaks at about 6.2, 10.7, 12.0 and 18.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.4.

In yet another embodiment, the invention encompasses a process forpreparing the above crystalline pemetrexed diacid. The process comprisescrystallizing pemetrexed diacid from a mixture comprising DMF as asolvent and a mixture of water and methanol as an anti-solvent.

In one embodiment, the invention encompasses crystalline pemetrexeddiacid characterized by data selected from the group consisting of: aPXRD pattern having peaks at about 9.0, 16.2, 18.1 and 26.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.5.

In yet another embodiment, the invention encompasses crystallinepemetrexed diacid characterized by data selected from the groupconsisting of: a PXRD pattern having peaks at about 7.7, 9.2, 16.7 and27.4 degrees two-theta±0.2 degrees two-theta; and a PXRD pattern asdepicted in FIG. 6.

In one embodiment, the invention encompasses a process for preparing theabove crystalline pemetrexed diacid. The process comprises admixingN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt of the following formula

and at least one base to obtain a solution, and adding the solution toan acid to obtain a suspension comprising the said crystallinepemetrexed diacid.

In another embodiment, the invention encompasses crystalline pemetrexeddiacid characterized by data selected from the group consisting of: aPXRD pattern having peaks at about 6.8, 11.9, 15.5 and 17.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.7.

In yet another embodiment, the invention encompasses a process forpreparing a pharmaceutically acceptable salt of pemetrexed diacidcomprising preparing any of the above crystalline pemetrexed diacid bythe processes of the invention, and converting them to thepharmaceutically acceptable salt of pemetrexed diacid.

In one embodiment, the invention encompasses a process for preparing alyophilized form of a pharmaceutically acceptable salt of pemetrexedcomprising preparing any of the above crystalline pemetrexed diacid bythe processes of the invention, and transforming them to the lyophilizedpharmaceutically acceptable salt of pemetrexed. Preferably, thepharmaceutically acceptable salt is pemetrexed disodium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 10.0, 10.3, 22.0 and 25.7 degrees two-theta±0.2degrees two-theta.

FIG. 2. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2degrees two-theta.

FIG. 3. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 5.8, 12.4, 18.6 and 24.6 degrees two-theta±0.2degrees two-theta.

FIG. 4. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 6.2, 10.7, 12.0 and 18.9 degrees two-theta±0.2degrees two-theta.

FIG. 5. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 9.0, 16.2, 18.1 and 26.9 degrees two-theta±0.2degrees two-theta.

FIG. 6. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 7.7, 9.2, 16.7, and 27.4 degrees two-theta±0.2degrees two-theta.

FIG. 7. illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 6.8, 11.9, 15.5 and 17.9 degrees two-theta±0.2degrees two-theta.

FIG. 8 illustrates an X-ray powder diffraction pattern of crystallinepemetrexed diacid characterized by an X-ray powder diffraction patternwith peaks at about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2degrees two-theta obtained in example 12.

DETAILED DESCRIPTION OF THE INVENTION

The invention addresses a need in the art by providing crystalline formsof pemetrexed diacid, as well as methods for their preparation.

The time periods described herein are time periods suitable forlaboratory-scale preparations. One of ordinary skill in the artunderstands that suitable time periods will vary based upon the amountsof reagents present, and can adjust the time periods accordingly.

The invention encompasses crystalline pemetrexed diacid characterized bydata selected from the group consisting of: an X-ray powder diffraction(“PXRD”) pattern having peaks at about 10.0, 10.3, 22.0 and 25.7 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted inFIG. 1. This crystalline pemetrexed diacid can be designated as Form A.

One of ordinary skill in the art is aware that there is a certain amountof experimental error inherent in powder X-ray diffraction (“PXRD”)techniques. See, e.g., U.S. PHARMACOPEIA, 387-89 (30th ed. 2007), herebyincorporated by reference. As to individual peaks, peak positions arereported over a range of ±0.2° 2θ to account for this experimentalerror. As to PXRD patterns in their entirety, the term “as depicted” ina particular figure is meant to account for this experimental error, aswell as for variations in peak position and intensity due to factorssuch as, for example, variations in sample preparation, instrumentation,and the skill of the operator of the instrument. A PXRD pattern “asdepicted” in a particular figure means that one of ordinary skill in theart, understanding the experimental error involved in powder X-raydiffraction techniques, would determine that the PXRD patterncorresponds to the same crystalline structure as the PXRD patterndepicted in the figure.

The crystalline pemetrexed diacid Form A may be further characterized bydata selected from a group consisting of: a weight loss of about 7.8% toabout 8.8% at a temperature up to 160° C., as measured by thermalgravimetric analysis (“TGA”), and an X-ray powder diffraction patternhaving peaks at about 5.6, 13.4, 16.8 and 25.1±0.2 degrees two-theta.

The crystalline pemetrexed diacid Form A is a hydrated form, andpreferably a dihydrated form. The water content of the crystallinepemetrexed diacid is about 7.7% by weight, as measured by the KarlFischer technique (“KF”).

In addition, the crystalline pemetrexed diacid Form A has less thanabout 10% by weight, more preferably less than about 5% by weight, andmost preferably less than about 1% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe done using the peak at 12.2 degrees two-theta±0.2 degrees two-theta.

The present invention also provides a process for preparing thecrystalline pemetrexed diacid Form A. The process comprisescrystallizing pemetrexed diacid from an aqueous solvent at a pH of about4.5.

Preferably, the crystallization comprises: dissolving pemetrexeddisodium in an aqueous solvent to obtain a solution, and adjusting thepH of the solution to about 4.5 to obtain a suspension comprising aprecipitate of the crystalline pemetrexed diacid Form A.

Typically, the aqueous solvent is water or a mixture of water and awater-miscible organic solvent. Suitable water-miscible organic solventsinclude, but are not limited to ethanol, methanol, and acetonitrile.Preferably, the aqueous solvent is water.

Typically, the pH of the solution is adjusted by adding an acid.Preferably, the acid is provided in a form of a diluted aqueoussolution. Preferably, the acid is HCl, HBr, H₂SO₄, trifluoroacetic acid,acetic acid, or p-toluenesulfonic acid, and more preferably HCl.Typically, the addition of the acid induces precipitation of thecrystalline pemetrexed diacid.

The crystallization may further comprise heating the suspension and thencooling the suspension. These additional process steps are believed toaid in crystal growth. Preferably, the suspension is heated to atemperature of about 60° C. to about 70° C., and more preferably about65° C. Preferably, the suspension is cooled to a temperature of about30° C. to about 20° C., and more preferably to about 24° C. Preferably,the suspension is cooled for about 3 to about 7 hours, and morepreferably about 5 hours.

Typically, the suspension is maintained to increase the yield of theprecipitated crystalline pemetrexed diacid. Preferably, the suspensionis maintained for about 8 to about 16 hours and more preferably forabout 10 hours, preferably, with agitation.

The obtained crystalline pemetrexed diacid may be recovered from thesuspension by any method known to a skilled artisan. Preferably, thecrystalline pemetrexed diacid is recovered from the suspension byfiltration. The recovered crystalline pemetrexed diacid may be washedwith water adjusted to a pH of about 4.4 to about 4.6, more preferablyabout 4.5, and dried. Preferably, the drying is performed under vacuum,more preferably at a pressure of about 18 mbar, at a temperature ofabout 35° C. to about 50° C., more preferably about 40° C. Preferably,the crystalline pemetrexed diacid is dried for about 10 to about 24hours, and more preferably for about 17 hours.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 5.7, 12.2, 17.2 and 18.4 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.2. This crystalline pemetrexed diacid can be designated as Form B.

The crystalline pemetrexed diacid Form B can be further characterized bydata selected from a group consisting of: a PXRD pattern having peaks atabout 11.5, 17.8, 22.8 and 26.7 degrees two-theta±0.2 degrees two-theta,and a weight loss of about 2.6% to about 3.8% at a temperature up to220° C., as measured by TGA.

The crystalline pemetrexed diacid Form B is a hydrated form ofpemetrexed diacid. The water content of the crystalline pemetrexeddiacid is about 2.5% to about 3.9% by weight, as measured by KF.

In addition, the crystalline pemetrexed diacid Form B has less thanabout 15% by weight, preferably less than about 10% by weight, and morepreferably less than about 5% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 10.0, 10.3, 22.0 and 25.7 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 10.0, 10.3, 22.0 and 25.7 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe done using any one of the peaks at 10.0 and 10.3 degreestwo-theta±0.2 degrees two-theta.

The invention further encompasses a process for preparing thecrystalline pemetrexed diacid Form B. The process comprises providing asuspension of pemetrexed diacid in an aqueous solvent having a pH ofabout 3, and adjusting the pH of the suspension to about 4.5.

Preferably, the process comprises: dissolving pemetrexed disodium in anaqueous solvent to form a solution, adjusting the pH of the solution toabout 3 to obtain a suspension, and adjusting the pH of the suspensionto about 4.5 to obtain a precipitate of the crystalline pemetrexeddiacid Form B.

Typically, the pH of about 3 is obtained by adding an acid to thesolution. Preferably, the acid is provided in the form of a dilutedaqueous solution. Preferably, the acid is HCl 1, HBr, H₂SO₄,trifluoroacetic acid, acetic acid, or p-toluenesulfonic acid, and morepreferably HCl. Typically, the addition of the acid inducesprecipitation of the crystalline pemetrexed diacid.

The process may further comprise heating the suspension, and thencooling the suspension, prior to adjusting the pH to about 4.5. Theseadditional process steps are believed to aid in crystal growth.Preferably, the suspension is heated to a temperature of about 60° C. toabout 70° C., and more preferably about 65° C. Preferably, thesuspension is cooled to a temperature of about 30° C. to about 20° C.,and more preferably to about 24° C. Preferably, the suspension is cooledfor about 3 to about 8 hours, and more preferably about 5 hours.

Typically, the suspension is maintained to increase the yield of theprecipitated crystalline pemetrexed diacid. Preferably, the suspensionis maintained for about 8 to about 16 hours, and more preferably about11.5 hours, preferably, with agitation.

The pH is typically adjusted to about 4.5 by adding a base to thesuspension. Preferably, the base is an alkali metal hydroxide, such assodium hydroxide, lithium hydroxide, or potassium hydroxide, and morepreferably sodium hydroxide. Preferably, the sodium hydroxide isprovided in a form of an aqueous solution. Preferably, the aqueoussolution is a diluted aqueous solution.

The above crystalline pemetrexed diacid may be recovered from thesuspension by any method known to a skilled artisan. Preferably, thecrystalline pemetrexed diacid is recovered from the suspension byfiltration. The recovered crystalline pemetrexed diacid may be washedwith water adjusted to a pH of about 4.4 to about 4.6, more preferably4.5, and dried. Preferably, the drying is performed under vacuum, morepreferably at a pressure of about 18 mbar, at a temperature of about 30°C. to about 80° C., more preferably about 40° C. Preferably, thecrystalline pemetrexed diacid is dried for about 10 to about 25 hours,and more preferably for about 17 hours.

The invention also encompasses another process for preparing thecrystalline pemetrexed diacid Form B. The process comprises slurrying inwater crystalline pemetrexed diacid characterized by data selected froma group consisting of: a PXRD pattern having peaks at about 6.2, 10.7,12.0 and 18.9 degrees two-theta±0.2 degrees two-theta, and a PXRDpattern as depicted in FIG. 4.

Preferably, the starting crystalline pemetrexed diacid is slurried inabout 6 to 9 volumes of water, i.e., 6 to 9 milliliters of water pergram of crystalline pemetrexed diacid. More preferably, the startingcrystalline pemetrexed diacid is slurried in about 7 to 8 volumes ofwater. Preferably, the starting crystalline pemetrexed is slurried at atemperature of about 50° C. Preferably, the slurrying is done for about1 to about 3 hours.

Typically, the heated slurry is then cooled. Preferably, the heatedslurry is cooled to a temperature of about 0° C. to about 24° C.Preferably, the cooling is conducted over a period of about 1 to 2hours. After cooling, the slurry can be further maintained for about 1to about 3 hours.

The obtained crystalline pemetrexed diacid may then be recovered fromthe slurry by any method known to one of ordinary skill in the art. Suchmethods include filtering the crystalline pemetrexed diacid from theslurry, followed by drying. Preferably, the drying is performed undervacuum with heating. Preferably, the drying is performed at atemperature of about 70° C. at a pressure of about 18 mbar, for about 18hours. The crystalline pemetrexed diacid Form B thus prepared isillustrated by the PXRD pattern shown in FIG. 8. The PXRD pattern ofFIG. 8 contains the characteristic peaks of pemetrexed diacid form B asdescribed above, as well as additional peaks at 6.0 and 12.6 degreestwo-theta±0.2 degrees two-theta.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 5.8, 12.4, 18.6 and 24.6 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.3. This crystalline pemetrexed diacid can be designated as Form C.

The crystalline pemetrexed diacid Form C can be further characterized bydata selected from a group consisting of: a PXRD pattern having peaks atabout 9.2, 11.7, 12.8 and 19.6 degrees two-theta±0.2 degrees two-theta;and a two-step weight loss, where the first is of about 2.3% at atemperature up to 140° C., due to loss of water, and the second, is ofabout 2.9% at a temperature up to 200° C., due to loss ofdimethylsulfoxide (“DMSO”), as measured by TGA.

The crystalline pemetrexed diacid Form C is a solvated form ofpemetrexed diacid, and preferably a DMSO solvate.

In addition, the crystalline pemetrexed diacid Form C has less than 15%by weight, more preferably less than 10% by weight, and most preferably,less than 5% by weight, of crystalline pemetrexed diacid characterizedby an X-ray powder diffraction pattern with peaks at about 5.7, 12.2,17.2 and 18.4 degrees two-theta±0.2 degrees two-theta. Typically, thecontent of crystalline pemetrexed diacid characterized by an X-raypowder diffraction pattern having peaks at about 5.7, 12.2, 17.2 and18.4 degrees two-theta±0.2 degrees two-theta in the above form isdetermined by PXRD. The determination by PXRD can be done using the peakat 17.2 degrees two-theta±0.2 degrees two-theta.

The invention also encompasses a process for preparing the crystallinepemetrexed diacid Form C. The process comprises crystallizing pemetrexeddiacid from a mixture comprising DMSO as a solvent and a mixture ofwater and at least one C₁₋₄ alcohol as an anti-solvent.

Typically, the crystallization is performed by combining the pemetrexeddiacid and DMSO to obtain a solution, and admixing with the anti-solventto precipitate the crystalline pemetrexed diacid Form C.

The starting pemetrexed diacid may be prepared according to any processknown to a skilled artisan. For example, the pemetrexed diacid can beprepared according to the process described in Org. Proc. Res. Dev.2005, pp. 738-742, which is incorporated herein by reference.

Typically, the solution of pemetrexed diacid in DMSO is provided byheating a combination of pemetrexed diacid and DMSO. Preferably, thecombination is heated to about 25° C. to about 75° C., and morepreferably about 65° C.

Preferably, the pemetrexed diacid is combined with the DMSO in a ratioof about 1:1 to about 1:3 g/mL, respectively.

Typically, the anti-solvent is admixed with the solution. Preferably,the anti-solvent and the solution are admixed at a temperature of about30° C. to about 65° C., and more preferably at about 40° C. to about 50°C. The anti-solvent is, preferably, added to the solution. Preferably,the anti-solvent is added to the solution drop-wise. Preferably, theanti-solvent is added drop-wise to the solution over a period of about 1hour to about 5 hours, and more preferably about 1 hour to about 2.5hours.

Suitable C₁₋₄ alcohols include, but are not limited to methanol,ethanol, isopropanol, propanol, isobutanol, and butanol. Preferably, themixture of water and a C₁₋₄ alcohol, is that of methanol and water.Preferably, the ratio of the C₁₋₄ alcohol and water in the anti-solventmixture is of about 1:3 to about 3:1 vol./vol., respectively. Typically,admixing the anti-solvent with the solution forms a suspensioncomprising a precipitate of the said crystalline pemetrexed diacid.

Usually, the suspension is maintained to increase the yield of theprecipitated crystalline pemetrexed diacid. Preferably, the suspensionis maintained at a temperature of about 30° C. to about 65° C.Preferably, the suspension is maintained for about 20 minutes to aboutthree hours, and more preferably for about 30 minutes to about 1.5hours. Preferably, the suspension is maintained while being stirred.

The yield of the crystalline pemetrexed diacid Form C may also beincreased by cooling the suspension to induce further precipitation ofthe crystalline pemetrexed diacid. Preferably, the suspension is cooledto a temperature of about 30° C. to about 0° C., and more preferably toabout 25° C. to about 10° C. Preferably, the cooling is performed over aperiod of about 1 to about 6 hours, and more preferably about 2 to about4 hours. Preferably, the cooled suspension is maintained for about 0.5to about 6 hours, and more preferably for about 2 to about 4 hours,prior to recovering the crystalline pemetrexed diacid.

The obtained crystalline pemetrexed diacid may be recovered by anymethod known to a skilled artisan. Preferably, the crystallinepemetrexed diacid is recovered from the suspension by filtration. Therecovered crystalline pemetrexed diacid may be washed and dried. Therecovered pemetrexed diacid may be washed with water or a mixture ofwater and methanol. The recovered pemetrexed diacid may be dried undervacuum with heating. Preferably, the recovered pemetrexed diacid isdried at a temperature of about 35° C. to about 50° C., at a pressure ofabout 18 mbar, for about 24 to about 72 hours.

The recovered crystalline pemetrexed diacid may optionally be furtherpurified by slurrying in the anti-solvent. Preferably, the recoveredcrystalline pemetrexed diacid is washed with the anti-solvent prior toslurrying it. The preferred anti-solvent for washing is water or amixture of water and methanol. Optionally, the washed crystallinepemetrexed diacid may be dried prior to slurrying it. The drying may bedone at a temperature of about 35° C. to about 45° C., and morepreferably about 40° C., under vacuum, preferably at a pressure of about18 mbar.

Preferably, the slurrying is performed at a temperature of about 5° C.to about 65° C., and more preferably at about 35° C. to about 50° C.Preferably, the slurrying is performed for about 0.5 hour to about 4hours, and more preferably for about 1 hour to about 2 hours.Preferably, the anti-solvent used for slurrying is selected from thegroup consisting of water, ethanol, methanol and mixtures thereof.

Typically, the slurry is cooled prior to recovering the purifiedcrystalline pemetrexed diacid Form C. Preferably, the slurry is cooledto a temperature of about 30° C. to about 5° C., and more preferablyabout 25° C. to about 10° C.

The purified crystalline pemetrexed diacid may be recovered from theslurry by any method known to a skilled artisan. Preferably, thepurified crystalline pemetrexed diacid is recovered from the slurry byfiltration. The recovered crystalline pemetrexed diacid may then bedried.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 6.2, 10.7, 12.0 and 18.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.4. This crystalline pemetrexed diacid can be designated as Form D.

The crystalline pemetrexed diacid Form D can be further characterized bydata selected from a group consisting of: a PXRD pattern having peaks atabout 13.9 and 17.4 degrees two-theta±0.2 degrees two-theta; and atwo-step weight loss; where the first is of about 1.5% to about 3.6% ata temperature up to 140° C., due to loss of water, and the second, is ofabout 8.6% to about 12.3% at a temperature up to 190° C., due to loss ofdimethylformamide (“DMF”), as measured by TGA.

The crystalline pemetrexed diacid Form D is a solvated form ofpemetrexed diacid, and preferably a DMF solvate.

The crystalline pemetrexed diacid Form D has less than about 10% byweight, more preferably less than about 5% by weight, and mostpreferably less than about 1% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe using any one of the peaks at 5.7, 17.2 and 18.4 degreestwo-theta±0.2 degrees two-theta.

The invention also encompasses a process for preparing the abovecrystalline pemetrexed diacid. The process comprises crystallizingpemetrexed diacid from a mixture comprising DMF as a solvent and amixture of water and methanol as an anti-solvent.

Typically, the crystallization is performed by combining the pemetrexeddiacid and the DMF to obtain a solution, and admixing with theanti-solvent to precipitate the crystalline pemetrexed diacid Form D.

Typically, the solution of pemetrexed diacid in DMF is provided byheating a combination of pemetrexed diacid and DMF. Preferably, thecombination is heated to about 30° C. to about 65° C., and morepreferably about 50° C.

Typically, the anti-solvent is admixed with the solution at atemperature of about 30° C. to about 65° C., and more preferably atabout 50° C. The anti-solvent is, preferably, added to the solution.Preferably, the anti-solvent is added to the solution drop-wise.Preferably, the anti-solvent is added drop-wise to the solution over aperiod of about 80 minutes.

Preferably, the ratio of the methanol and water in the anti-solventmixture is of about 1:3 to about 3:1 vol./vol, respectively. Typically,admixing the anti-solvent with the solution forms a suspensioncomprising a precipitate of the said crystalline pemetrexed diacid.

Usually, the suspension is maintained to increase the yield of theprecipitated crystalline pemetrexed diacid. Preferably, the suspensionis maintained at a temperature of about 30° C. to about 55° C.Preferably, the suspension is maintained for about 2 to about 6 hours,and more preferably for about 3 hours. Preferably, the suspension ismaintained while being stirred.

The yield of the crystalline pemetrexed diacid may also be increased bycooling the suspension to induce further precipitation of thecrystalline pemetrexed diacid. Preferably, the suspension is cooled to atemperature of about 20° C. to about 30° C., and more preferably about28° C. Preferably, the cooling is performed over a period of about 1 toabout 3 hours, and more preferably about 2 hours. Preferably, the cooledsuspension is maintained for about 0.5 to about 6 hours, and morepreferably for about 2 to about 4 hours, prior to recovering thecrystalline pemetrexed diacid.

The obtained crystalline pemetrexed diacid may be recovered by anymethod known to a skilled artisan. Preferably, the crystallinepemetrexed diacid is recovered from the suspension by filtration. Therecovered crystalline pemetrexed diacid may be washed and dried. Therecovered crystalline pemetrexed diacid may be washed with water or amixture of water and methanol. The recovered crystalline pemetrexeddiacid may be dried under vacuum with heating. Preferably, the recoveredpemetrexed diacid is dried at a temperature of about 30° C. to about 50°C., and preferably about 40° C., under vacuum, preferably at a pressureof about 18 mbar.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 9.0, 16.2, 18.1 and 26.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.5. This crystalline pemetrexed diacid can be designated as Form E.

The crystalline pemetrexed diacid Form E can be further characterized bydata selected from the group consisting of: a PXRD pattern having peaksat about 5.8, 6.9, 12.0, 18.8, and 19.6 degrees two-theta±0.2 degreestwo-theta; and a two-step weight loss; where the first is of about 2.5%at a temperature up to 100° C., due to loss of water, and the second, isof about 11.7% at a temperature up to 200° C., due to loss of DMF, asmeasured by TGA.

The crystalline pemetrexed diacid Form E is a solvated form ofpemetrexed diacid, and preferably a DMF solvate.

In addition, the crystalline pemetrexed diacid Form E has less thanabout 15% by weight, more preferably less than about 10% by weight, andmost preferably less than about 5% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe done using the peak at 17.2 degrees two-theta±0.2 degrees two-theta.

The invention further encompasses a process for preparing thecrystalline pemetrexed diacid Form E. The process comprisescrystallizing pemetrexed diacid from a mixture comprising DMF as asolvent, and ethanol as an anti-solvent.

Typically, the crystallization is performed by combining the pemetrexeddiacid and the DMF to obtain a solution, and admixing with ethanol toprecipitate the crystalline pemetrexed diacid Form E.

Typically, the solution of pemetrexed diacid in DMF is provided byheating a combination of pemetrexed diacid and DMF. Preferably, thecombination is heated to about 40° C. to about 60° C., and morepreferably about 50° C.

Typically, the anti-solvent is admixed with the solution at atemperature of about 40° C. to about 60° C., and more preferably atabout 50° C. The anti-solvent is, preferably, added to the solution.Preferably, the anti-solvent is added to the solution drop-wise.Preferably, the anti-solvent is added drop-wise to the solution over aperiod of about 0.5 hour to 1.5 hours, and more preferably about 45minutes.

Preferably, the ethanol is absolute ethanol. Typically, admixing theanti-solvent with the solution forms a suspension comprising thecrystalline pemetrexed diacid Form E.

The yield of the crystalline pemetrexed diacid Form E may be increasedby cooling the suspension to further induce precipitation of thecrystalline pemetrexed diacid. Preferably, the suspension is cooled to atemperature of about 30° C. to about 0° C., and more preferably to aboutroom temperature.

The yield of the crystalline pemetrexed diacid may also be increased bycombining the cooled suspension with an additional amount of ethanol toinduce further precipitation of the crystalline pemetrexed diacid. Thetotal amount of ethanol can be, optionally, added at one portion. Afterthe addition of the second amount of the ethanol, the ratio between theDMF solvent and ethanol is preferably, of about 1:1 to about 1:10,vol./vol., respectively, more preferably, of about 1:5.5 vol./vol.,respectively. The new suspension, obtained after the addition of thesecond amount of ethanol, is then preferably maintained again, prior torecovering the product. Preferably, the new suspension is maintained forabout 2 to about 24 hours, more preferably, of about 18 hours.

The obtained crystalline pemetrexed diacid may be recovered by anymethod known to a skilled artisan. Preferably, the crystallinepemetrexed diacid is recovered from the suspension by filtration. Therecovered crystalline pemetrexed diacid may be washed and dried. Therecovered pemetrexed diacid may be washed with ethanol. The recoveredpemetrexed diacid may be dried under vacuum with heating. Preferably,the recovered pemetrexed diacid is dried at a temperature of about 35°C. to about 50° C., at a pressure of about 18 mbar, for about 24 toabout 72 hours.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 7.7, 9.2, 16.7 and 27.4 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.6. This crystalline pemetrexed diacid can be designated as Form F.

The crystalline pemetrexed diacid Form F can be further characterized bydata selected from the group consisting of: a PXRD pattern having peaksat about 14.2, 15.4, 18.5, and 20.5 degrees two-theta±0.2 degreestwo-theta; and a weight loss of about 0.2% to about 0.3% at atemperature up to 190° C., as measured by TGA.

The crystalline pemetrexed diacid Form F is an anhydrous form ofpemetrexed diacid. As used herein, unless otherwise defined, the term“anhydrous” when referring to pemetrexed diacid means a substance havinga weight loss not more than 1% by TGA.

The crystalline pemetrexed diacid Form F has less than about 10% byweight, more preferably less than about 5% by weight, and mostpreferably less than about 1% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe done using the peak at 12.2 degrees two-theta±0.2 degrees two-theta.

The invention also encompasses a process for preparing the crystallinepemetrexed diacid Form F. The process comprises admixingN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt of the following formula

and at least one base to obtain a solution, and adding the solution toan acid to obtain a suspension comprising the said crystallinepemetrexed diacid.

The startingN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt can be obtained, forexample, according to the process disclosed in U.S. Pat. No. 6,262,262,hereby incorporated by reference.

Typically, theN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt is first combined withwater and then with the base to obtain the solution. The base can be anorganic or inorganic base. Preferably, the organic base is triethylamineor diisopropylamine. Preferably, the inorganic base is sodium hydroxide,potassium hydroxide, sodium carbonate or lithium hydroxide, and morepreferably sodium hydroxide. The inorganic base can be used in its solidform or in a form of an aqueous solution.

Typically, combining the base and theN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt provides a salt ofpemetrexed diacid, which is soluble in water.

The solution of the salt has a basic pH, preferably, of about 11 toabout 14. Combining the base and theN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt is typically exothermic,and, thus, is performed with cooling. Preferably, the cooling is to atemperature of about 20° C. to about 0° C., more preferably, to about 2°C.

The acid may be a mineral acid or an organic acid. Preferably, themineral acid is H₂SO₄, HCl, or HBr. Preferably, the organic acid ismethanesulfonic acid or toluenesulfonic acid. More preferably, the acidis HCl. Typically, the acid is provided in the form of an aqueoussolution. The aqueous solution may be generated by combining aconcentrated acid with water.

Adding the solution to the acid is typically exothermic. To reduce theexotherm, the solution and/or the acid may be cooled during theaddition. The solution may also be added drop-wise to the acid to reducethe exotherm. The cooling is, preferably, to a temperature of about 20°C. to about 0° C., more preferably, to about 2° C. Preferably, thedrop-wise addition is done over a period of about 15 to about 45minutes, more preferably, of about 20 minutes.

Typically, the solution is added to the acid while stirring to ensurethe occurrence of the reaction. Typically, the acid neutralizes thesalt, providing a suspension comprising free pemetrexed diacid.

The suspension is then typically heated. Preferably, the suspension isheated to a temperature of about 60° C. to about 80° C., and morepreferably about 70° C. Preferably, the heating is done for about 1 hourto about 4 hours, and more preferably for about 2 hours.

Typically, the suspension is cooled prior to recovering the crystallinepemetrexed diacid Form F. The suspension is preferably cooled to atemperature of about 30° C. to about 10° C., and more preferably toabout 20° C. Preferably, the cooling is done for a period of about 1.5hours to 3 hours, and more preferably for about 2 hours. Typically, thecooled slurry is maintained while stirring for a period of about 3 toabout 6 hours, more preferably, for about 4 hours.

The obtained crystalline pemetrexed diacid may be recovered by anymethod known to a skilled artisan. Preferably, the crystallinepemetrexed diacid is recovered from the suspension by filtration. Therecovered crystalline pemetrexed diacid may be washed and dried. Therecovered pemetrexed diacid may be washed with water. The recoveredpemetrexed diacid may be dried under vacuum with heating. Preferably,the recovered pemetrexed diacid is dried at a temperature of about 70°C., at a pressure of about 18 mbar, for about 10 to about 16 hours.

The invention also encompasses crystalline pemetrexed diacidcharacterized by data selected from the group consisting of: a PXRDpattern having peaks at about 6.8, 11.9, 15.5 and 17.9 degreestwo-theta±0.2 degrees two-theta; and a PXRD pattern as depicted in FIG.7. This crystalline pemetrexed diacid can be designated as Form G.

The crystalline pemetrexed diacid Form G may be further characterized bydata selected from a group consisting of: a PXRD pattern having peaks atabout 8.9, 20.5, and 24.1 degrees two-theta±0.2 degrees two-theta; and aweight loss of about 0.6% to about 0.9% at a temperature up to 120° C.,as measured by TGA.

The crystalline pemetrexed diacid Form G is an anhydrous form ofpemetrexed diacid.

In addition, the crystalline pemetrexed diacid Form G has less thanabout 15% by weight, more preferably less than about 10% by weight, andmost preferably less than about 5% by weight, of crystalline pemetrexeddiacid characterized by an X-ray powder diffraction pattern having peaksat about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degreestwo-theta. Typically, the content of crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2 degrees two-thetain the above form is determined by PXRD. The determination by PXRD canbe done using the peak at 12.2 degrees two-theta±0.2 degrees two-theta.

The invention also encompasses a process for preparing the crystallinepemetrexed diacid Form G. The process comprises heating a crystallineform of pemetrexed diacid selected from the group consisting of:crystalline pemetrexed diacid characterized by an X-ray powderdiffraction pattern having peaks at about 5.7, 12.2, 17.2 and 18.4degrees two-theta±0.2 degrees two-theta; crystalline pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.8, 12.4, 18.6 and 24.6 degrees two-theta±0.2 degrees two-theta;crystalline pemetrexed diacid characterized by an X-ray powderdiffraction pattern having peaks at about 9.0, 16.2, 18.1 and 26.9degrees two-theta±0.2 degrees two-theta; and mixtures thereof.

Typically, the crystalline form of pemetrexed diacid is heated to atemperature of about 160° C. to about 200° C., preferably about 180° C.to about 200° C., to effect conversion to the said crystallinepemetrexed diacid.

The crystalline form of pemetrexed diacid can be heated in one step orgradually. Gradual heating preferably includes two stages of heating.Preferably, the first stage of heating is to a temperature of about 100°C. to about 160° C. Preferably, the first stage of heating is for about30 minutes to about 1 hour. Preferably, the second stage of heating isto a temperature of about 180° C. to about 200° C. Preferably, thesecond stage of heating is for about 20 to about 40 minutes, morepreferably, for about 0.5 hour.

The invention also encompasses an additional process for preparing thecrystalline pemetrexed diacid Form G. The process comprises dryingcrystalline pemetrexed diacid characterized by an X-ray powderdiffraction pattern having peaks at about 10.0, 10.3, 22.0 and 25.7degrees two-theta±0.2 degrees two-theta at a temperature of about 200°C. for about 30 minutes.

The invention also encompasses another process for preparing thecrystalline pemetrexed diacid Form G. The process comprises dryingcrystalline pemetrexed diacid characterized by an X-ray powderdiffraction pattern having peaks at about 6.2, 10.7, 12.0 and 18.9degrees two-theta±0.2 degrees two-theta at a temperature of about 200°C. for about 30 minutes.

The invention also encompasses a process for preparing apharmaceutically acceptable salt of pemetrexed diacid comprisingpreparing any of the above crystalline pemetrexed diacid by theprocesses of the invention, and converting them to the pharmaceuticallyacceptable salt of pemetrexed diacid. Preferably, the pharmaceuticallyacceptable salt is pemetrexed disodium. The conversion can be done, forexample, according to the process disclosed in U.S. publication No.2003/0216416, hereby incorporated by reference.

The invention also encompasses a process for preparing a lyophilizedform of a pharmaceutically acceptable salt of pemetrexed comprisingpreparing any of the above crystalline forms of pemetrexed diacid by theprocesses of the invention, and converting them to the lyophilizedpharmaceutically acceptable salt of pemetrexed. Preferably, thepharmaceutically acceptable salt is pemetrexed disodium. This conversionmay be done, for example, according to the process disclosed in U.S.Published Application No. 2008/0139810, (U.S. application Ser. No.11/893,234, filed Aug. 14, 2007), as well as U.S. application Ser. Nos.60/847,291, filed Sep. 25, 2006; 60/855,139, filed Oct. 30, 2006;60/880,179, filed Jan. 11, 2007; and 60/958,326, filed Jul. 2, 2007, allof which are incorporated herein by reference.

Any of the above crystalline forms of pemetrexed diacid can be convertedinto a lyophilized pharmaceutically acceptable salt of pemetrexed diacidby a process comprising: combining the crystalline form of pemetrexeddiacid, an agent capable of forming a pharmaceutically acceptable saltof pemetrexed, and a solvent comprising water or a mixture of water anda solvent suitable for lyophilization to obtain a mixture comprising apharmaceutically acceptable salt of pemetrexed; and removing the solventby lyophilization to obtain a lyophilized pharmaceutically acceptablesalt of pemetrexed; wherein the pharmaceutically acceptable salt ofpemetrexed is not isolated prior to the lyophilization process; and thepharmaceutically acceptable salt of pemetrexed is a di-base-additionsalt of pemetrexed.

As used herein, unless otherwise, defined, an “agent capable of forminga pharmaceutically acceptable salt of pemetrexed” refers to an agentthat is capable of forming a base-addition salt of pemetrexed.Base-addition salts include, but are not limited to, alkali or alkalineearth metal salts, such as sodium, potassium, lithium, and calciumsalts.

Preferably, the agent capable of forming a pharmaceutically acceptablesalt of pemetrexed is an alkali (preferably sodium) or alkaline earthmetal hydroxide, carbonate, phosphate, or sulfate. More preferably, theagent capable of forming a pharmaceutically acceptable salt ofpemetrexed is an alkali or alkaline earth metal hydroxide, and mostpreferably sodium hydroxide.

In a preferred embodiment, initially, the crystalline form of pemetrexeddiacid is combined with the solvent to obtain a first mixture.Preferably, the solvent is water. When a mixture of water and a solventsuitable for lyophilization is used, the solvent suitable forlyophilization may include, but is not limited to, tert-butanol,dimethylsulfoxide, or 1,4-dioxane. Preferably, the solvent suitable forlyophilization is tert-butanol.

The first mixture is then admixed with an alkali or alkaline earth metalhydroxide to obtain the mixture comprising the pharmaceuticallyacceptable salt of pemetrexed.

Preferably, the alkali or alkaline earth metal hydroxide is NaOH, KOH,LiOH, or Ca(OH)₂, and more preferably, NaOH.

Preferably, the alkali or alkaline earth metal hydroxide is added to thefirst mixture. Preferably, the mixture is a solution.

Typically, to obtain the pharmaceutically acceptable salt of pemetrexedfrom the crystalline form of pemetrexed diacid, at least about 1 moleequivalent of alkali or alkaline earth metal hydroxide per moleequivalent of the starting crystalline form of pemetrexed diacid isused. Preferably, the alkali hydroxide is used in an amount of about 1to about 3 mole equivalents per mole equivalent of the startingcrystalline form of pemetrexed diacid or salt thereof.

The alkali hydroxide may be in solution or solid form. Preferably, thealkali or alkaline earth metal hydroxide is in the form of an aqueoussolution. Preferably, the aqueous solution of the alkali or alkalineearth metal hydroxide is a standard solution. As used herein, unlessotherwise defined, the term “standard solution” refers to a solutionhaving a known concentration, where the concentration is determined byvarious methods known to a skilled artisan, such as titration withacids. Preferably, the standard solution of the alkali or alkaline earthmetal hydroxide has a concentration of about 0.5 M to about 4 M, morepreferably, of about 2 M.

Preferably, admixing the first mixture and the alkali or alkaline earthmetal hydroxide solution is performed at a temperature of about 1° C. toabout 100° C., more preferably at about 10° C. to about 60° C., and mostpreferably at about 15° C. to about 40° C.

As a skilled artisan will appreciate, complete dissolution or a stablepH value of about 7.0 to 7.5, or, more preferably, 7.1 to 7.2, is anindication that the reaction has completed.

The process for preparing lyophilized pharmaceutically acceptable saltof pemetrexed may further comprise a process of adjusting the pH toobtain a pH of about 7.0 to about 10.0, preferably, of about 7.0 toabout 9.0, more preferably, of about 7.0 to about 8.0, and mostpreferably, of about 7.0 to about 7.5, prior to lyophilizing thesolution comprising the pharmaceutically acceptable salt of pemetrexed.The pH can be adjusted by admixing the solution comprising thepharmaceutically acceptable salt of pemetrexed with alkali hydroxide orwith any one of the starting materials, depending on the pH of thesolution. Typically, the pH measurement is done by using a pH-meter.

Optionally, a dispersing agent may be added to the mixture beforeremoving the solvent. Preferably, the dispersing agent is a sugar suchas lactose, fructose or mannitol. Preferably, the sugar is mannitol.Preferably, the dispersing agent is present in an equimolar amount inweight relative to the amount of the pharmaceutically acceptable salt ofpemetrexed.

Having described the invention with reference to certain preferredembodiments, other embodiments will become apparent to one skilled inthe art from consideration of the specification. The invention isfurther defined by reference to the following examples. It will beapparent to those skilled in the art that many modifications, both tomaterials and methods, may be practiced without departing from the scopeof the invention.

EXAMPLES Experimental Methodology (Physical)

Powder X-Ray Diffraction:

Powder X-ray diffraction was performed on a ARL X-ray powderdiffractometer model X'TRA-030, with a Peltier detector. Round standardaluminum sample holders with round zero background quartz plates wereused. The scanning parameters were as follows: Range: 2-40 deg. 2θ,continuous Scan, Rate: 3 deg./min. The accuracy of peak positions isdefined as +/−0.2 degrees due to experimental differences such asinstrumentation and sample preparation.

Thermal Gravimetric Analysis:

TGA/SDTA 851^(e), Mettler Toledo, Sample weight 7-15 mg.

Heating rate: 10° C./min., In N₂ stream: flow rate=50 ml/min

Scan range: 30-250° C. or 30-280° C.

Example 1 Preparation of Crystalline Pemetrexed Diacid Characterized byan X-Ray Powder Diffraction Pattern Having Peaks at about 10.0, 10.3,22.0 and 25.7 Degrees Two-Theta±0.2 Degrees Two-Theta

A flask was charged withN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid disodium salt (23.89 g) and water (478 ml) and stirred for 20minutes at 24° C., to achieve complete dissolution. The pH of theresulting solution was adjusted to about 4.5 by the addition of dilutedhydrochloric acid, after which abundant solid formation was observed.The resulting suspension was then heated to 65° C. for 25 minutes, wasslowly cooled to 24° C. over a period of 5 hours, and was then stirredat 24° C. for 10 hours. The solid was filtered from the suspension andwashed two times (2×50 ml) with water adjusted to pH 4.5 withhydrochloric acid. The wet solid was dried at 40° C. under vacuum (18mbar) for 16.5 hours to afford the title compound as a white, fine solid(7.20 g). The X-ray powder diffraction pattern of the dry material wasmeasured and is illustrated in FIG. 1.

Example 2 Preparation of Crystalline Pemetrexed Diacid Characterized byan X-Ray Powder Diffraction Pattern Having Peaks at about 5.7, 12.2,17.2 and 18.4 Degrees Two-Theta±0.2 Degrees Two-Theta

A flask was charged withN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid disodium salt (12.77 g) and water (240 ml) and stirred at 24° C. toachieve complete dissolution. The pH of the resulting solution wasadjusted to about 3.0 by the addition of hydrochloric acid, after whichabundant solid formation was observed. The resulting suspension was thenheated to 65° C. for 35 minutes, was slowly cooled to 24° C. over aperiod of 5 hours, and was then stirred at 24° C. for 11.5 hours. The pHof the suspension was then adjusted to about 4.5 by the addition of 2.0Msodium hydroxide, and the suspension was stirred at 24° C. for 50minutes. The solid was filtered from the suspension and washed two times(2×50 ml) with water adjusted to pH 4.5 with hydrochloric acid. The wetsolid was dried at 40° C. under vacuum (18 mbar) for 15.5 hours toafford the title compound as a white-grey solid (8.32 g). The X-raypowder diffraction pattern of the dry material was measured and isillustrated in FIG. 2.

Example 3 Preparation of Crystalline Pemetrexed Diacid Characterized byan X-Ray Powder Diffraction Pattern Having Peaks at about 5.8, 12.4,18.6 and 24.6 Degrees Two-Theta±0.2 Degrees Two-Theta

A flask was charged withN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid (98.22% HPLC purity) (10.0 g) and dimethylsulfoxide (25 ml), heatedto 65° C. and stirred until complete dissolution. Methanol (37.5 ml) andwater (37.5 mL) was then added drop-wise to the solution over a periodof about 2.5 hours. The resulting suspension was stirred for 1 hour at65° C. and then was cooled to 22° C. over a period of about 2.5 hours.The suspension was filtered and the isolated solid was washed with amixture of water (50 ml) and methanol (50 mL). The solid was then driedat 40° C. under vacuum (18 mbar) for about 16 hours, to afford pemetexeddiacid (7.62 g) in 99.16% purity (HPLC).

A 2 g sample of the dry pemetrexed acid was slurried in 15 mL of waterto form a suspension. The suspension was then heated at 50° C. for 1 hand then slowly cooled to ambient temperature and filtered. Theresulting solid was dried in the oven at 80° C. under vacuum (18 mbar)for about 16 hours to afford the title compound in 99.46% purity (HPLC).The X-ray powder diffraction pattern of the dry material was measuredand is illustrated in FIG. 3.

Example 4 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 6.2, 10.7, 12.0 and18.9 Degrees Two-Theta±0.2 Degrees Two-Theta

A flask was charged withN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid (99.00% HPLC purity) (3.64 g) and dimethylformamide (7.3 ml),heated to 50° C. and stirred until complete dissolution. A mixture ofwater (10.9) and methanol (18.2 ml) was then added drop-wise to thesolution over a period of about 80 minutes. The obtained suspension wasstirred for 30 minutes at 50° C. and then cooled to 30° C. over a periodof about 2 hours. The suspension was filtered and the solid was washedwith water (20 ml).

The wet solid was dried at 40° C. under vacuum (18 mbar) for about 72hours to afford the title compound as a light-blue solid (3.02 g) in99.32% purity (HPLC). The X-ray powder diffraction pattern of the drymaterial was measured and is illustrated in FIG. 4.

Example 5 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 9.0, 16.2, 18.1, and26.9 Degrees Two-Theta±0.2 Degrees Two-Theta

Pemetrexed Diacid (3.0 g) was dissolved in DMF (6.0 ml), the solutionwas heated at 50° C. for 45 minutes, absolute EtOH (18.0 ml) was addeddrop-wise over 15 minutes and the slurry was heated for 30 minutes more.The mixture was cooled to room temperature and other absolute EtOH (15.0ml) was added to the suspension. The suspension was kept under stirringfor 18 h, was filtered and washed with absolute EtOH (3×3.0 ml). The wetcake was dried at 40° C. under vacuum for 72 h, resulting 2.88 g (96.0%)of the pemetrexed diacid. The PXRD pattern of the dried pemetrexeddiacid was measured and illustrated in FIG. 5.

Example 6 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 7.7, 9.2, 16.7, and27.4 Degrees Two-Theta±0.2 Degrees Two-Theta

5 g ofN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic Acid Salt was suspended at 2° C. in50 mL water. 50 mL of aqueous sodium hydroxide (2M), previously cooledto 2° C., were added and the mixture was stirred for 1.5 hours at 2° C.Complete dissolution was observed. The solution was then addeddrop-wise, at 2° C., over 20 minutes, to a solution of 3.0 mL aqueoushydrochloric acid (37%) in 30 mL of water and the pH was corrected from3.9 to 4.1 with aqueous sodium hydroxide 0.1N. The resulting suspensionwas stirred at 2° C. for 30 min. and heated at 70° C. for two hours.After cooling to 24° C. in 2 hours, the suspension was filtered and thesolid was dried in the oven at 70° C. under vacuum (18 mbar) to yieldthe titled compound (75.17%). The PXRD pattern of the dried pemetrexeddiacid was measured and illustrated in FIG. 6.

Example 7 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 6.8, 11.9, 15.5 and17.9 Degrees Two-Theta±0.2 Degrees Two-Theta

250 mg sample of crystalline pemetrexed characterized by a PXRD patternhaving peaks at about 5.7, 12.2, 17.2 and 18.4 degrees two-theta±0.2degrees two-theta was kept in an oven at 160° C. for 1 hour and after itwas kept at 200° C. for 30 minutes. The PXRD pattern of the driedpemetrexed diacid was measured and illustrated in FIG. 7.

Example 8 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern with Peaks at about 6.8, 11.9, 15.5 and 17.9Degrees Two-Theta±0.2 Degrees Two-Theta

A 200 mg sample of the product of example 3 was kept in an oven at 100°C. for 30 minutes and after it was kept at 180° C. for 30 minutes. TheX-ray powder diffraction pattern of the heat-treated material wasmeasured.

Example 9 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern with Peaks at about 6.8, 11.9, 15.5 and 17.9Degrees Two-Theta±0.2 Degrees Two-Theta

A 200 mg sample of the product of example 5 was kept in an oven at 100°C. for 30 minutes and after it was kept at 180° C. for 30 minutes. TheX-ray powder diffraction pattern of the heat-treated material wasmeasured.

Example 10 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 6.8, 11.9, 15.5 and17.9 Degrees Two-Theta±0.2 Degrees Two-Theta

A sample of crystalline pemetrexed diacid characterized by a PXRDpattern having peaks at about 10.0, 10.3, 22.0 and 25.7 degreestwo-theta±0.2 degrees two-theta (about 150 mg) was kept in an oven at200° C. for 30 minutes. The X-ray powder diffraction pattern of thedried crystalline pemetrexed diacid was measured.

Example 11 Preparation of Pemetrexed Diacid Characterized by an X-RayPowder Diffraction Pattern Having Peaks at about 6.8, 11.9, 15.5 and17.9 Degrees Two-Theta±0.2 Degrees Two-Theta

A sample of crystalline pemetrexed diacid characterized by a PXRDpattern having peaks at about 6.2, 10.7, 12.0 and 18.9 degreestwo-theta±0.2 degrees two-theta (about 150 mg) was kept in an oven at200° C. for 30 minutes. The X-ray powder diffraction pattern of thedried crystalline pemetrexed diacid was measured.

Example 12 Preparation of Crystalline Pemetrexed Diacid Characterized byan X-Ray Powder Diffraction Pattern with Peaks at about 5.7, 12.2, 17.2and 18.4 Degrees Two-Theta±0.2 Degrees Two-Theta

Crystalline pemetrexed diacid characterized by an X-ray powderdiffraction pattern having peaks at about 6.2, 10.7, 12.0 and 18.9degrees two-theta±0.2 degrees two-theta was slurried in water (20 mL) at50° C. for one hour, and then cooled to 26° C. over a period of about 2hours. The suspension was then filtered. The wet solid was washed withwater and dried at 40° C. under vacuum (18 mbar) for about 16 hours toafford the title compound as a light-blue solid (3.02 g) in 99.32%chemical purity (HPLC). The X-ray powder diffraction pattern of the drymaterial was measured and is illustrated in FIG. 8.

Example 13 LyophilizedN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid disodium salt

5 grams ofN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid was dissolved in 1 L of distilled water and 11.698 ml of a 2.0 Msolution of sodium hydroxide was added to the solution. Mannitol (10 g)was then added to the solution and dissolved. The solution was thenfiltered through a bacterial filter and dried in a freeze-drier toafford 15.5 g of title compound as a white solid.

Example 14 Preparation ofN-[4-[2-(2-Amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid disodium salt

A flask was charged with crudeN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamicacid (4 g), water (28 ml) and NaOH (3 equivalents) at 25° C. Completedissolution was obtained. The pH was corrected to 10.0 with HCl 1M andacetone (120 mL) was added drop wise over a period of 50 min. Theobtained suspension was cooled to 2° C. in one hour, stirred at 2° C.for 10 hours and filtered. The solid was washed with acetone (30 mL) anddried at 40° C. under vacuum (18 mbar) for about 16 hours affording thetitle compound.

Example 15 Preparation ofN-(4-[2-(2-amino-4,7-Dihydro-4-oxo-1H-Pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl)-L-GlutamicAcid Diethyl Ester p-Toluenesulfonic Acid Salt (based upon Example 6 ofU.S. Pat. No. 6,262,262

A flask is charged with 1.93 g of4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoicacid and 13.5 mL of dimethylformamide. The slurry is stirred 20 minutesand 1.94 g N-methylmorpholine is added. The mixture is cooled to 5° C.and 1.46 g chlorodimethoxytriazine is added all at once. The mixture isstirred for 1 h and then 1.99 g L-glutamic acid diethyl esterhydrochloride is added. The resulting reaction mixture is then allowedto warm to ambient temperature. The end of the reaction is detected byHPLC after about 1 h. At that point 36 mL of water and 36 mL ofdichloromethane are added to the reaction mixture, which is stirred for15 minutes. The layers are then allowed to separate. The organic phaseis collected and concentrated to 13 g and then replaced by 60 mL ofabsolute ethanol. The solution is heated at 75° C. and 3.16 gp-toluenesulfonic acid dissolved in 55 mL of ethanol absolute is addedto the solution drop wise. The resulting slurry is refluxed for an hour,then cooled to ambient temperature and filtered. The wet cake is washedwith 25 mL ethanol, and dried in the oven at 40° C., under vacuumovernight, to yield 3.66 g of the title compound.

What is claimed is:
 1. A crystalline form of pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 7.7, 9.2, 16.7 and 27.4 degrees two-theta±0.2 degrees two-theta.2. The crystalline pemetrexed diacid of claim 1, further characterizedby an X-ray powder diffraction pattern having peaks at about 14.2, 15.4,18.5, and 20.5 degrees two-theta±0.2 degrees two-theta.
 3. Thecrystalline pemetrexed diacid of claim 1, wherein the crystallinepemetrexed diacid is anhydrous.
 4. The crystalline pemetrexed diacid ofclaim 1, further characterized by a weight loss of about 0.2% to about0.3% at a temperature up to 190° C., as measured by thermogravimetricanalysis.
 5. The crystalline pemetrexed diacid of claim 1, having lessthan about 10% by weight of a crystalline form of pemetrexed diacidcharacterized by an X-ray powder diffraction pattern having peaks atabout 5.7, 12.2, 17.2, and 18.4 degrees two-theta±0.2 degrees two-theta.6. A process for preparing a crystalline form of pemetrexed diacidaccording to claim 1 said process comprising: a) admixingN-(4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]-benzoyl)-L-glutamicacid diethyl ester p-toluenesulfonic acid salt of the following formula

and at least one base to obtain a solution, and b) adding the solutionto an acid to obtain a suspension comprising the crystalline pemetrexeddiacid.
 7. The process of claim 6, wherein the base is an organic base.8. The process of claim 7, wherein the organic base is selected from thegroup consisting of triethylamine, diisopropylamine, and mixturesthereof.
 9. The process of claim 6, wherein the base is an inorganicbase.
 10. The process of claim 9, wherein the organic base is selectedfrom the group consisting of sodium hydroxide, potassium hydroxide,sodium carbonate and lithium hydroxide, and mixtures thereof.
 11. Theprocess of claim 6, wherein the solution has a pH of about 11 to about14.
 12. The process of claim 6, wherein the acid is a mineral acid. 13.The process of claim 12, wherein the mineral acid is selected from thegroup consisting of H₂SO₄, HCl, HBr, and mixtures thereof.
 14. Theprocess of claim 6, wherein the acid is an organic acid.
 15. The processof claim 14, wherein the organic acid is selected from the groupconsisting of methanesulfonic acid, toluene sulfonic acid, and mixturesthereof.